This invention relates to steel rule die cutting and particularly to a method and apparatus for cutting single and stacked layers of compressible materials such as foam plastic by means of a stationary steel rule die.
Steel rule dies are commonly used for cutting cloth and clothlike materials such as natural textiles, and synthetic materials such as vinyl. Steel rule dies are particularly advantageous in the repetitive cutting of specific shapes such as shirt collars, automobile interior panels and the like. In brief, a steel rule die typically comprises a base or backing board in which a groove matching the pattern to be cut is formed, and a length of steel rule embedded in the board with a sharpened exposed edge extending upwardly tberefrom. The die is used in combination with a cutting table and a press which may either be single-cut or progressive feed.
A problem arises when it is necessary or desirable to cut relatively thick but compressible materials such as foam-backed vinyl, foam rubber, and plastic foam. A stack or a particularly thick single layer of such material is sufficiently unstable that an accurate cut is often not possible using- conventional techniques.
One approach to the more accurate cutting of foam materials is disclosed in U.S. Pat. Nos. 3,790,154, 3,765,289 and 3,815,221, all assigned to Gerber Garment Technology, Inc. of East Hartford, Conn. These patents, and other related patents assigned to Gerber, disclose a vacuum table which is used primarily to hold sheet material in place while it is cut by a two-axis single blade jigsaw type cutter. According to these patents, a sheet of Mylar or other air impervious material can placed over a stack of compressible materials such that the vacuum table creates a vacuum under the sheet to pull downwardly on the sheet and maintain the entire stack in a stable, compressed condition during the cutting process. In a further Gerber U.S. Pat. No. 4,060,016, the jigsaw type cutter is replaced by a rotatable turret carrying a plurality of blanking dies which are selectively rotated into position and driven downwardly through an air impervious sheet and through the stacked materials to form a stack of cut patterns corresponding to the shape of the particular die selected.
In all of these patented systems the board on which the stacked material is located must be capable of receiving the penetrations of the reciprocating knife as well as maintaining a vacuum for the principal purpose of holding the stack in place and for the secondary purpose of evacuating the volume under the air impervious sheet.
All of these patented arrangements also suffer from the disadvantage that the air impervious sheet is cut in the process of cutting the stacked material layers with consequent loss of vacuum and thereby a loss of stability of the stack. And whereas certain of the Gerber patents describe means for "healing" the cut in the air impervious sheet behind the cutting member, these healing arrangements unduly complicate the overall cutting apparatus and/or are not totally successful in preventing loss of vacuum with a consequent loss of stability of the stack.
It has been proposed to use steel rule blanking or cutting dies with air evacuation compression so as to facilitate and improve the use of such dies to cut compressible materials. These proposals have involved the use of an air impervious cover or shroud positioned over a stack of compressible material positioned on the steel rule upper edge to define a vacuum chamber, and means for evacuating the vacuum chamber to compress and reduce the thickness of a stack of layers before cutting the layers with the rule. Such an arrangement is shown in U.S. Pat. No. 4,543,862 assigned to the assignee of the present application. Whereas the method and apparatus disclosed in U.S. Pat. No. 4,543,862 is generally satisfactory for the cutting of compressible materials and has achieved significant commercial acceptance, the procedure of this patented process, whereby a large shroud of air impervious material is positioned over the stack of compressible material to form the vacuum chamber, is labor intensive and therefore contributes significantly to the overall cost of the process. Further, the shroud tends to wear with repeated usage and must eventually be replaced with the result that the materials cost of the process is thereby increased.